1. Field of the Invention
The present invention relates to a ferule into which an optical fiber is inserted which has a core covered with one or plural protecting films and not covered with its end, and a method of processing the end of the optical fiber.
2. Description of the Related Art
In a prior art, where optical fibers are connected to each other and a light emitting/receiving element is connected to an optical fiber, a ferule was securely attached to the end of the optical fiber.
Now referring to FIG. 16, an more detailed explanation will be given of the prior art. FIG. 16 is a sectional view of the attachment state between an optical fiber and a ferule, which is disclosed in JP-A-9-90163.
As seen from FIG. 16, a ferule, generally 1 is composed of an inner small-diameter cylinder 2 and an outer outer-diameter cylinder 3, which are stepped. The outer cylinder 3 is provided with a flange 4 on its outer wall. The flange 4 is adapted to receive urging force of a spring (not shown) mounted in an optical connector housing (not shown).
An optical fiber 5 has a core 6 covered with two sheathing films, an inner primary sheath 7 and an outer secondary sheath 8.
The small diameter cylinder 2 has an inner diameter that is slightly larger than the diameter of the core 6 of the optical fiber 5. The larger diameter cylinder 2 has also an inner diameter that is slightly larger than the outer diameter of the secondary sheath 8.
As seen from FIG. 16, the optical fiber 5 has an end which is covered with no sheathing film. The optical fiber 5, with an adhesive (two-liquid mixed epoxy resin adhesive in the above prior art) being applied to the outer surface of the optical fiber inclusive of the end, is inserted in the ferule 1. In this state, when the structure thus formed is heated for a prescribed time at a prescribed temperature, the optical fiber 5 and ferule 1 are coupled with each other with sufficient adhesive force.
The two-liquid mixed epoxy adhesive used in the prior art can provide great adhesive force. However, use of this adhesive requires a large number of working steps for processing or trimming for the end of the optical fiber 5, i.e. application of an adhesive, insertion of the optical fiber, wiping off of the excessive amount of adhesive, heating/hardening of the adhesive, etc. This influences the production cost.
Changes in the mixing ratio of the two adhesive liquids will vary the adhesive intensity. This will make the quality control complicate.
Further, heating/hardening of the adhesive which satisfies the condition of e.g. 100.degree. C. and one hour requires a comparatively large heating device. Therefore, a sufficient working space must be assured. A limited working space cannot increase the number of times of heating/hardening, which leads to reduction in the productivity.